Many types of probes have a surface region forming the active sensing area. Typical of such probes are capacitive, optical, electromagnetic, and acoustical probes to name a few. The surface region determines at least partly the probes sensitivity and spatial resolution. As the sensing area increases, so does sensitivity but at the expense of spatial resolution. For many applications it is desirable to have the high sensitivity advantage of a large sensing area but with a spatial resolution corresponding to a much smaller sensing area.
Many applications such as the semiconductor wafer quality control and production processes call for accurate and reliable data representative of a preselected characteristic of an object such as the thickness and flatness of one or more semiconductor wafers. The novel Wafer Flatness Station disclosed in co-pending utility patent application Ser. No. 572,695, invented by the same inventive entity and assigned to the same assignee as the instant invention, incorporated herein by reference, for example, includes a capacitive sensing head, and means including an actuator associated therewith that are co-operative to sequentially measure the thickness of preselected points of a semiconductor wafer, and to automatically provide data in response thereto that is representative of the flatness of the wafer. The capacitive sensing head includes at least one probe the spatial resolution of which is determined by its characteristic physical dimension. In regions of the object to be tested remote from its actual physical boundaries, such as for the thickness sensing of semiconductor wafers at points thereof that are remote from its edge, such a head is operative to provide highly accurate and reliable data. The confidence level of the data is limited, however, for those points located adjacent to the physical boundaries of the object that are within a characteristic physical dimension of its boundaries, such as wafer points located within a probe width of the edge of the wafer. One known technique to improve the confidence-level for such data points is to actually reduce the characteristic physical dimension of the probe. This technique is disadvantageous, however, due to the difficulty in and associated costs for manufacturing miniature probes, and due to the reduced signal-to-noise levels characteristicly produced by such miniature probes, among other things.